Return nested List from web api using Entity Framework and navigation properties

Question

I'm trying to return a JSON with a nested list using Navigation properties but I keep getting null in the 'Usuario' collection here's the output.

 [
  {
    "$id": "1",
    "id": 1,
    "encabezado": "Como llamar a un metodo en c#",
    "cuerpo": "Estoy intentando llamar un metodo metodo() pero no puedo alguna sugerencia xD?",
    "points": 0,
    "Usuario": null,
    "Respuestas": []
  },
  {
    "$id": "2",
    "id": 2,
    "encabezado": "Como cambiar conection String",
    "cuerpo": "Es posible cambiar el conection string en asp.net si ya esta creada?",
    "points": 1,
    "Usuario": null,
    "Respuestas": []
  }
]

here's my .edmx

And finally this is where I have the web api

namespace AskTecProject.Controllers
{
    public class QuestionController : ApiController
    {
        [HttpGet]
        public List<Pregunta> GetQuestions()
        {
            using (asktecdbEntities entities = new asktecdbEntities())
            {
                List<Pregunta> p = entities.Usuarios.Where(m => m.id.Equals(1)).SelectMany(m => m.Preguntas).ToList<Pregunta>();
                return p;

            }
        }
    }
}

I got his query from Getting a related collection but I'm still having trouble with this, I'll appreciate any help

Sergey Berezovskiy · Accepted Answer · 2016-12-06 09:02:57Z

2

You should use Eager Loading:

List<Pregunta> preguntas = entities.Usuarios
       .Where(u => u.id.Equals(1))
       .SelectMany(u => u.Preguntas)
       .Include(p => p.Usuario) // here
       .ToList<Pregunta>();

Side note - seems like all your Preguntas entities will have same Usuario entity with id = 1. Also you don't need to specify generic parameter for ToList method - parameter should be inferred.

edited Dec 6, 2016 at 9:02

answered Dec 6, 2016 at 8:57

Sergey Berezovskiy

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1 Comment

Daniel Moreno Over a year ago

Thank you Sergey, I was having trouble for a second, cause I didn't had Systems.Data.Entity imported and I was getting the Include method from other library. But It works great, thanks again.

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